1. Field of the Invention
The present invention relates to a force transmission assembly used, in particular, in piloting an aircraft, and it also relates to a control assembly including such an assembly.
2. Brief Description of the Related Art
An aircraft, such as a helicopter or an airplane, generally includes a control assembly equipped with at least one lever, commonly referred to as a “stick”. The pilot operates the lever so as to transmit instructions to the direction control members of the aircraft, such as rotary wing blades. The lever is connected to the direction control members via at least one force transmission assembly.
It is known for use to be made of such a transmission assembly that includes at least one torsion spring box made up of one or more torsion springs making it possible to define the relationship for shift as a function of torque applied by the lever. Such a relationship is linear relative to the variation in the value of the angle between a final position and an initial position of the lever.
Nevertheless, the movement in rotation of the lever is limited by the capacity of the spring to twist. If it is desired to have high amplitude variation in the angle of rotation of the lever, it is necessary to increase the length of the torsion spring. Alternatively, provision may be made to increase the diameter of the spring working in torsion. In both situations, the overall size of the spring box and, as a result, of the transmission assembly, is necessarily increased.
Document DE-A-35 34 935 proposes a force transmission assembly designed to be incorporated into a clutch. In that example, a wheel, that is mounted to rotate about a hub shaft, is provided with a drive lever and with two opposite cams that bear against rollers fastened to a stationary support. Under the action of those cams, the wheel moves in translation along the hub shaft, while driving in translation a pusher that bears against brake disks, and while also compressing a spring interposed between the pusher and an annular end of the hub shaft. That pusher is constrained in rotation with the hub shaft by a through pin, with non-negligible angular backlash and non-negligible friction. That solution does not therefore enable an angular position of the lever to be caused to correspond accurately to a transmitted torque value, due to the backlash and to the friction hysteresis. That makes that solution inappropriate for the above-mentioned field of piloting an aircraft. In other words, the transmission assembly of DE-A-35 34 935 is neither designed nor intended to cause a position of its lever to correspond to a given force on that lever, in that the forces relative to the lever can be quite different depending on the direction of actuation of the transmission assembly, namely depending on whether it is actuated in a clutching direction or in a declutching direction.